Silver Nanodendrites Research Articles

Trace detection of herbicides by SERS technique, using SERS-active substrates fabricated from different silver nanostructures deposited on silicon

In this report we present the initial results of the use of different silver nanostructures deposited on silicon for trace detection of paraquat (a commonly used herbicide) using the surface-enhanced Raman scattering (SERS) effect. More specifically, the SERS-active substrates were fabricated from silver nanoparticles (AgNPs) deposited onto the flat surface of a silicon wafer (AgNPs@Si substrate), as well as on the surface of an obliquely aligned silicon nanowire (SiNW) array (AgNPs@SiNWs substrate), and from silver nanodendrites (AgNDs) deposited onto the flat surface of a silicon wafer (AgNDs@Si substrate). Results showed that with the change of the structure of the SERS-active substrate, higher levels of SERS enhancement have been achieved. Specifically, with the fabricated AgNDs@Si substrate, paraquat concentration as low as 1 ppm can be detected.

Electrochemical synthesis, characterisation and phytogenic properties of silver nanoparticles

This work exemplifies a simple and rapid method for the synthesis of silver nanodendrite with a novel electrochemical technique. The antibacterial activity of these silver nanoparticles (Ag NPs) against pathogenic bacteria was investigated along with the routine study of optical and spectral characterisation. The optical properties of the silver nanoparticles were characterised by diffuse reflectance spectroscopy. The optical band gap energy of the electrodeposited Ag NPs was determined from the diffuse reflectance using Kubelka–Munk formula. X-ray diffraction (XRD) studies were carried out to determine the crystalline nature of the silver nanoparticles which confirmed the formation of silver nanocrystals. The XRD pattern revealed that the electrodeposited Ag NPs were in the cubic geometry with dendrite preponderance. The average particle size and the peak broadening were deliberated using Debye–Scherrer equation and lattice strain due to the peak broadening was studied using Williamson–Hall method. Surface morphology of the Ag NPs was characterised by high-resolution scanning electron microscope and the results showed the high degree of aggregation in the particles. The antibacterial activity of the Ag NPs was evaluated and showed unprecedented level antibacterial activity against multidrug resistant strains such as Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumonia and Escherichia coli in combination with Streptomycin.

Electrocatalytic dechlorination of chloroacetic acids on silver nanodendrites electrode

Silver nanodendrites were successfully prepared by electrodeposition on the glassy carbon electrode. The effects of synthesis parameters such as concentrations of reagents and applied potentials on the morphology and structure of silver nanodendrites have been investigated. Electrochemical experiments showed that silver nanodendrites electrode had extraordinary electrocatalytic activity toward the dechlorination of chloroacetic acids. The electrocatalytic hydrogenolysis mechanism was the main pathway for the dechlorination of chloroacetic acids.

Silver nanodendrite modified graphene rotating disk electrode for nonenzymatic hydrogen peroxide detection

Although silver nanostructures have been widely used for H2O2 detection, the development of silver based nanomaterials with higher performance toward H2O2 detection is still needed. In this work, metallic silver nanodendrite (AgND) modified reduced graphene oxide (rGO) electrode with open pore structure was prepared by an electrodeposition method and used for H2O2 detection. The rotating disk electrode (RDE) was used to study the convective diffusion effect of H2O2 to the electrode. The performance of the AgND/rGO electrode toward H2O2 detection significantly depends on the rotation rate of the electrode. At the rotation rates of 0 and 100rpm, the as-fabricated electrode could not detect H2O2. At higher rotation rates, wide linear ranges of detected H2O2 concentrations with a determination coefficient R2 of over 0.99 are found to be 1–100, 0.5–100, 0.1–100, and 0.05–30mM at the electrode rotation rates of 500, 1000, 2000, and 6000rpm, respectively. The LOD values determined at a signal-to-noise ratio of ca. 3 are about 100, 50, 30, and 10μM at 500, 1000, 2000, and 6000rpm, respectively. The as-fabricated electrode can detect diluted H2O2 in milk demonstrating its potential sensing application.

Electrochemical determination of dissolved oxygen based on three dimensional electrosynthesis of silver nanodendrites electrode

In this paper, a highly sensitive electrochemical sensor for dissolved oxygen was prepared. A glassy carbon electrode was modified with silver nanodendrites that were synthesized by electrochemical deposition on the electrode without the use of a surfactant or template. The electrode displayed efficient electrocatalytic reduction of dissolved oxygen to form hydroxy ions via a four-electron reduction pathway, and a significant decrease in the respective overvoltage. The sensor responded linearly to dissolved oxygen in the 1.0–66.7 μM concentration range, and had a remarkably good sensitivity (0.169 μA μM−1) at an applied potential of −300 mV (vs. Ag/AgCl). The lower detection limit was 0.043 μM (at the signal-to-noise ratio of 3), and the response time was 5 s. The good performance was attributed to the enlarged electro-active surface of the dendritic silver nanostructures and to the efficiency of electron transfer between dissolved oxygen and the electrode. The sensor also showed good reproducibility, long-term stability, and relative good selectivity.

Photochemical assisted formation of silver nano dendrites and their application in amperometric sensing of nitrite

Herein, we describe a photochemical route for the synthesis of silver (Ag) dendrites nanostructure using phenothiazine (PTZ) as a reductant as well as stabilizer without any extra control viz. surfactant, pH etc. This hybrid material derived from nanoscale silver capped with phenothiazine and its oxidation product (PTZH) has been explored for the development of a highly sensitive electro-sensor of nitrite ions. Further, a possible reaction mechanism for the formation of the silver dendrites nanostructure has also been proposed. The synthesized hybrid material (Ag–PTZH) has been characterized by UV-visible spectroscopy, cyclic voltammetry, transmission electron microscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy. This hybrid material modified electrode efficiently catalyzes the electrochemical oxidation of nitrite at the potential of 0.44 V vs. AgCl/Ag and shows a linear response towards nitrite ion sensing with 2.43 μA μM−1 sensitivity and 2.3 nM limit of detection at a S/N (signal-to-noise ratio) of 3. The electrochemistry behind this sensing of nitrite is probably due to high connectivity throughout the silver dendrites nanostructure capped with phenothiazine and its oxidation product which exhibits high electron transfer kinetics via interaction of Ag–PTZH with oxygen atoms of NO2−.

Dendritic silver nanostructures obtained via one-step electrosynthesis: effect of nonanesulfonic acid and polyvinylpyrrolidone as additives on the analytical performance for hydrogen peroxide sensing

The electrochemical deposition of silver nanodendrites (AgNDs) on pure graphite sheet (PGS) electrodes, both in the absence of surfactant/templates and in the presence of 1-nonanesulfonic acid (NS) or polyvinylpyrrolidone (PVP) additives, is reported. The synthesis carried out without additives and with NS produced a bigger amount of large size AgNDs (dimension of 1–5 μm), with scarce influence played by NS, while the deposition with PVP favoured the formation of smaller spherical particles (with average diameter below 150 nm). The performances of the electrodes towards the electroreduction of H2O2 were investigated by chronoamperometry at −0.4 V and at more cathodic applied potentials (−0.6 and −0.8 V). The electrodes fabricated without additives and in the presence of NS displayed similar performances, while those fabricated with PVP exhibited significantly lower sensitivity. This suggests that AgNDs present enhanced electrocatalytic activity in respect to the spherical aggregates, since the Ag amount deposited on PGS was practically the same. The best amperometric responses among those recorded at −0.4 V in PBS (pH 6.7) exhibited a linear range extending from 0.1 to 3.5 mM, a detection limit of about 20 μM and a sensitivity close to 200 mA M−1 cm−2. The proposed electrodes display sensitivities which are markedly better than those reported in the literature for similar Ag-based sensors.

Controllable synthesis of silver nanodendrites on copper rod and its application to hydrogen peroxide and glucose detection

Silver nanodendrites were synthesized on Cu rods by a simple and facile displacement reaction without using any surfactants. The morphologies were investigated by scanning electron microscopy (SEM). The phase analysis of the dendritic nanostructure was revealed by X-ray diffraction (XRD). The element analysis was characterized by energy dispersive X-ray spectroscopy (EDS). Then a novel Ag nanodendrites/Cu rod electrode (named Ag NDS/CRE) based non-enzymatic hydrogen peroxide (H2O2) and glucose (GO) sensor was fabricated and evaluated by cyclic voltammetry (CV) and typical amperometric response (I–t) method. Exhilaratingly, the electrode shows significant electrocatalytic activity toward the reduction of H2O2 and oxidation of GO. Its advantage lies in its wide linear range from 0.2 mM to 19.2 mM for the detection of H2O2 with a low detection limit of 0.1 μM (S/N = 3) and also has a good response for GO with a linear range from 0.02 mM to 7.4 mM with the optimized detection limit of 0.1 μM (S/N = 3). The response time of the proposed electrode is less than 3 s. What's more, the proposed sensor displays excellent selectivity, good stability, and satisfying repeatability.

Space-confined fabrication of silver nanodendrites and their enhanced SERS activity

Here we report a controllable method based on electrodeposition to fabricate Ag nanodendrites (NDs) on a microwell patterned electrode. The microwell patterns on the ITO electrode are fabricated via the microcontact printing technique. By varying the microwell size and electrodeposition time, the morphology of metal deposits on the microwell patterned ITO electrode can be tuned from boulders to dendrites. At the edge of the microwells, the current density was strengthened, which incurs rapid nucleation. The nucleus develops into dendrites because of Mullins-Sekerka instability. However, only boulders were observed at the center of microwells. By reducing the size of the microwells, only NDs were fabricated due to the edge effect. On the basis of understanding the underlying mechanism for dendritic growth in a confined space, our method is used for fabricating other noble metal (Au, Pt) nanodendrites. The controllable synthesis of Au and Pt NDs indicates the universality of this method. Compared with Ag film obtained from electron beam evaporation, the as-prepared Ag NDs exhibit highly enhanced surface-enhanced Raman scattering (SERS) sensitivity when they are used to detect rhodamine 6G (R6G). This approach provides a very controllable, reliable and general way for space-confined fabricating the noble metal nanodendrite arrays which show great promise in catalysis, sensing, biomedicine, electronic and magnetic devices.

Biomimetic formation of chicoric-acid-directed luminescent silver nanodendrites

In this work, we report the formation of well-defined silver nanodendrites via biomineralization under mild conditions in a single step, in the presence of the plant phytohormone chicoric acid (CA), a well-known HIV-I integrase inhibitor. CA played a dual role as reductant as well as directed the growth of the nanodendrites, which were found to grow primarily in the [111] and [200] directions. In addition to the formation of highly ordered hierarchical structures, the formed Ag nanodendrites were found to exhibit luminescence, as observed by confocal microscopy. This study not only demonstrates a new method for the preparation of luminescent silver nanodendrites using a simple, environmentally friendly biological method, but also indicates the ability of CA, a potent HIV-integrase inhibitor, to interact with silver ions which may shed light on its potential for additional biomedical and biosensor applications.

Facile, template-free synthesis of silver nanodendrites with high catalytic activity for the reduction of p-nitrophenol

Here we report a facile, surfactant-free and template-free synthesis process of highly uniform dendritic silver nanostructures with high catalytic activity for the reduction of p-nitrophenol. By controlling the concentration of AgNO3 aqueous solution and the reaction time, various shapes of silver nanodendrites (SNDs) could be obtained easily. The effects of different parameters such as concentrations of the reagents and reaction time on the morphology and structure of as-prepared tree-like nanostructures have also been investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Also, the X-ray photoelectron spectroscopy (XPS) has been used to identify the oxidation state of SNDs. In addition, the catalytic activity of the as-prepared SNDs samples at 200mM AgNO3 aqueous solution was evaluated by a redox reaction of p-nitrophenol in the presence of an excess amount of NaBH4. It was found that the highly symmetrical SNDs with roughly 60–120nm in stem and branch diameter and 3–12μm in length obtained after 120s reaction time do have higher catalytic activity than other SNDs prepared at different reaction time, several times stronger catalytic activity in the sodium borohydride reduction of p-nitrophenol to p-aminophenol, compared to some other silver nanoparticles reported in literature. The crystallinity provided by X-ray diffraction (XRD) analysis indicates that the improvement of the crystallinity is also very crucial for SNDs’ catalytic activities. The SNDs are very promising catalytic candidates for the reduction of p-nitrophenol because of easily simple preparation route and high catalytic activity.

Easy and Large Scale Synthesis Silver Nanodendrites: Highly Effective Filler for Isotropic Conductive Adhesives

Dendritic silver (Ag) nanoparticles have been successfully prepared by an easy and large scale liquid-phase reduction method. Transmission electron microscope (TEM), scanning electron microscope (SEM), and x-ray diffraction (XRD) have shown that the Ag particles prepared by this method are pure and with uniform dendritic morphology. The bulk resistivity and bonding strength of isotropic conductive adhesives (ICAs) filled with Ag nanodendrite and micrometer-sized Ag have been measured. The results show that the dendritic morphology of Ag nanoparticles has a strong effect for improving the reinforcement of the composite electrical performance. ICA filled with small amounts of Ag nanodendrites exhibits lower bulk resistivity and higher bonding strength than ICA filled with micrometer-sized Ag. When ICA is filled with 50 wt.% micrometer-sized Ag and 10 wt.% Ag nanodendrites, the bulk resistivity is 1.3 × 10−4 Ω cm, and the bonding strength reaches 18.9 MPa.

Hierarchical silver nanodendrites: One-step preparation and application for SERS

Without using any other reducing reagents or templates, a one-step approach for synthesizing dendritic Ag nanostructure by the treatment of sliver ions only in the presence of silk fibroin biomacromolecule is described. The morphology and structure of as-prepared silver nanodendrite are characterized, and its application for surface-enhanced Raman scattering (SERS) is also investigated. It has been found that the morphology of as-prepared Ag dendrite is dependent on the reaction duration, but not the concentration of sliver ions in the reaction process. SERS study shows that the silver nanodendrites give an intensive and enhanced Raman scattering when pyridine is used as a probing molecule. It is suggested that silk fibroin provides dual reductant and structure-directing roles to promote sliver ions forming shape-controlled nanostructures in high yield.

Electrodeposited silver nanodendrites electrode with strongly enhanced electrocatalytic activity

Highly uniform dendritic silver nanostructures as a new electrode material, have been synthesized by electrodeposition on the glassy carbon (GC) electrode with assistance of polyethylene glycol 400 (PEG-400) as a soft template, to achieve a superior electrocatalyst with enhanced detection sensitivity in electroanalysis compared to conventional bulk Ag electrodes. The effects of the growth conditions such as concentrations of the reagents and applied potentials on the morphology and structure of as-prepared tree-like nanostructures have also been investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). In the silver nanodendrites (AgNDs), the diameter of the trunk is around 100–200 nm with length up to 10–40 μm, and the length of its branches can reach 10 μm. In addition, the electrocatalytic behavior of this modified electrode was exploited as a sensitive detection system for the reduction of RDX high explosive, hydrogen peroxide and hexacyanoferrate (HCF) by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Also, the obtained results were compared to multiwalled carbon nanotubes (MWCNTs) and bulk silver electrodes. These studies show that the nanodendritic silvers significantly increase the electron-transfer rate of the electrochemical reactions by as much as 1–2 orders of magnitude.

A green method for synthesis of silver nanodendrites

A simple, green method was developed for the synthesis of silver nanodendrites by an aqueous chemical route. This method involves the reduction of silver nitrate with absolute alcohol using polyvinyl pyrrolidone (PVP) as the surfactant. UV–vis absorption spectra, X-ray diffraction patterns (XRD) and energy dispersive spectrometry (EDS) suggest the formation of Ag nanoparticles. Transmission electron microscopy (TEM) images show the shape and sizes of the nanoparticles. During the synthesis, it was found that the morphology and size distribution of the as-prepared silver nanoparticles varied with the concentration of the precursor metal salts, reaction time and surfactant ratios. The formation mechanism of Ag nanodendrites was determined based on the investigation of the above reaction parameters. Simple methods, nontoxic chemicals and environmentally benign solvents make this synthesis ideally suited for industrial production.

Hot spots in highly Raman-enhancing silver nano-dendrites

A convenient strategy is demonstrated for placing C60 nanoclusters in hot spots between neighbouring arms of silver nano-dendrites leading to intense surface-enhanced Raman scattering (SERS) enhancement. The finite difference time domain calculations indicate that the dendrite-like model pattern may demonstrate a high quality SERS property owing to the ‘metal/nanoclusters/metal’ hot geometries. Further calculations provide useful guidelines for the synthesis of hot dendritic geometries and further increasing the enhancement factor of the SERS.

Time dependant evolution of silver nanodendrites

We report the synthesis of silver nanodendrites, with an elongated central backbone and distinguished branches. This method involves the reduction of silver nitrate with formamide using polyvinyl pyrrolidone as the surfactant. The evolution of the dendritic nanostructures after 30 days was due to the variation of the concentration of the reactants. At low PVP concentration isotropic silver nanoparticles are visible in the transmission electron microscopy (TEM) images. As the concentration is increased anisotropic particles are observed with the appearance of dendrites at the highest concentration. The morphological evolution is confirmed by the optical measurements.

Starch vermicelli template-assisted synthesis of size/shape-controlled nanoparticles

Size- and shape-controlled syntheses of silver and gold nanoparticles have been successfully developed using partially hydrolyzed starch vermicelli templates as green nanoreactors for the growth of nanoparticles. Mung bean vermicelli is of interest due to the higher amylose content and its transparency, allowing the formation of coloured particles on the vermicelli to be observed. The as-prepared silver and gold nanoparticles were characterized by UV–Visible spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The carbonization of as-prepared vermicelli at 200 °C, 300 °C, and 500 °C was carried out to investigate nanoparticles embedded in the starch vermicelli templates. TEM of carbonized samples revealed the interesting patterns of gold nanorods and silver nanowire-liked assemblies along with carbon nanotubes. The carbonization of silver nanoparticles at 500 °C resulted to the loss of starch vermicelli capping nanoparticles and this led to the higher diffusion rate of nanoparticles to generate silver nanodendrites on TEM images. XRD data of carbonized yellow and purple silver nanoparticles revealed the presence of silver nanoparticles and a mixture of silver and silver chloride nanoparticles, respectively. This approach offers a great potential to design new fine structures of vermicelli and utilize its structure as a template for the large-scale synthesis of size- and shape-controlled silver and gold nanoparticles for chemical and biological applications.

Dendritic Nanostructures of Silver: Facile Synthesis, Structural Characterizations, and Sensing Applications

Silver nanodendrites are synthesized by a simple surfactant-free method using a suspension of zinc microparticles as a heterogeneous reducing agent. Structural characterizations suggest the preferential growth along 100 and 111 directions by oriented attachment of silver nanocrystals in the diffusion limit, leading to the formation of silver nanodendrites 20-30 nm in stem and branch diameter and 5-50 microm in length. Surface-enhanced Raman scattering studies show that the silver nanodentrites give an intensive and enhanced Raman scattering when pyridine was used as a probing molecule. We have also demonstrated that the silver nanodendrites increase the sensitivity of an electrochemical glucose biosensor by as much as 1-2 orders of magnitude.